Beta HCG affects diagnosis of Down's syndrome - birth defect

Down's syndrome :: Beta HCG affects diagnosis of Down's syndrome - birth defect

Pregnant women who are vegetarians have increased levels of a hormone called free beta-hCG, which may lead to an incorrect diagnosis of Down's syndrome in their developing baby, Taiwanese researchers report. This suggests that higher beta-hCG test values need to be established for such women.

The test differences between non-vegetarian and vegetarian mothers largely disappeared when the latter had normal serum levels of vitamin B12, according to the report published in the American Journal of Obstetrics and Gynecology.

The findings are based on a study of 98 vegetarian and 122 non-vegetarian women who were pregnant. Reference values for beta-hCG and a related blood test, alpha-fetoprotein, were derived from a previously surveyed group of 6,312 pregnant women who had healthy babies.

The beta-HCG levels for the vegetarian group were higher than that of a reference group, lead author Dr. Po-Jen Cheng, from the Chang Gung Memorial Hospital in Taipei, and colleagues note. In contrast, the levels in the non-vegetarian group were comparable to that of the reference group.

These beta-HCG differences resulted in an incorrect Down's syndrome screening rate in the vegetarian group of 17 percent, significantly higher than the 5 to 6 percent rates seen in the other groups. Alpha-fetoprotein levels were slightly higher in the vegetarian group compared with the reference group.

Elevated beta-hCG levels were mostly confined to women with low vitamin B12 levels, Cheng and colleagues found. The alpha-fetoprotein level was not associated with the vitamin B12 level.

Until new reference values can be established, Down's syndrome screening in for pregnant vegetarians is more efficient if the screening is performed using ultrasound instead of measuring hCG levels, the investigators conclude.